1. Field of the Invention
The present invention relates to an electrical and mechanical system for steering the steered (i.e., steerable) wheels of an automobile vehicle. The steering system includes a steering wheel mounted on a steering column which is connected to a steering rack for the steered wheels.
2. Description of the Prior Art
In prior art steering systems as currently fitted to automobile vehicles the steering column 1 is always mechanical, as shown in FIG. 1, with an upper column part 4 carrying the steering wheel 2, the position of which is generally adjustable, and an intermediate shaft 6 between the upper column part 4 and the steering box 7 of the steering rack 3 with its rack 18 and pinion 17. The intermediate shaft 6 is connected to the upper column part 4 and to the steering box 7 by universal joints. Power steering 8 may be provided, and can be electrical. The above types of steering column have many drawbacks in terms of comfort and safety. This is because they do not have any means of returning the steering wheel to the center position. Also, the power steering is not matched to the driver. In the safety field, the above types of steering column have the major disadvantage of transferring impact to the steering wheel in the event of an accident because of the rigid connection between the steering wheel and the steered wheels.
The aim of the present invention is to propose an automobile vehicle steering system which avoids the drawbacks described hereinabove and in particular those due to the rigid connection between the steering wheel and the steered wheels.
According to the invention, the automobile vehicle steering system includes a steering column, a steering wheel and a steering rack for the steered wheels of the automobile vehicle. The steering column has an upper column part and an intermediate column part. The upper column part is connected at a first end to the steering wheel and at a second end to an upper end of the intermediate column part. The intermediate column part is connected by its lower end to the steering rack for the steered wheels of the automobile vehicle.
The intermediate column part comprises two connections : a mechanical connection and an electrical connection. The mechanical connection and the electrical connection are disposed in parallel such that :
the mechanical connection is connected to the second end of the upper column part and to the steering rack,
and the electrical connection is connected to the second end of the upper column part and to the steering rack.
This arrangement is accomplished so that under normal driving conditions the mechanical connection and the electrical connection function simultaneously and in the event of interruption of the electrical power supply the remaining mechanical connection is used to steer the automobile vehicle on its own.
According to the invention, the electrical connection includes :
a sensor sensing the demanded torque for steering the steered wheels,
an electromechanical power converter commanding the displacement of the steering rack for the steered wheels,
a central control unit connected to the torque sensor and to the electromechanical power converter,
so that the central control unit receives an electrical signal from the torque sensor and analyzes the demanded torque in order to send to the electromechanical power converter an electrical command and control signal for the force furnished by the electromechanical power converter.
According to the invention, the mechanical connection includes :
a mechanical cable system,
an upper connecting assembly for connecting the mechanical cable system to the upper steering column part,
a lower connecting assembly for connecting the mechanical cable system to the steering rack for the steered wheels. In the electrical connection, the electromechanical power converter is either a DC electric motor with brushes, or a brushless synchronous DC electric motor, or an asynchronous AC electric motor, or a variable reluctance synchronous electric motor.
According to the invention, the electromechanical power converter can be connected to the steering rack in different ways. In one arrangement, the electric motor is connected to a pinion which drives a rack on the steering rack.
In another arrangement, the electric motor is connected to a screw and nut system, the nut is attached to the rotor of the motor and the screw is on the steering rack.
In another arrangement, the electric motor is connected to the gear of a rack-and-pinion steering box which drives a rack on the steering rack.
Advantageously, in the electrical connection, the sensor sensing the demanded torque for steering the steered wheels is on the upper steering column part. In other forms of electrical connection, the sensor sensing the demanded torque for steering the steered wheels is on the pinion of the rack-and-pinion steering box, which provides a torque closer to that demanded by the steered wheels.
To improve the electrical connection, an actuator is disposed on the upper steering column part. The actuator is adapted to provide feedback between the steered wheels and the steering wheel and it is connected to the central control unit. Preferably, the feedback actuator is an electric motor.
According to the invention, in one embodiment of the mechanical connection, the mechanical cable system includes a cable operating in traction and in compression according to the direction of rotation of the steering wheel.
In a different mechanical connection structure, the mechanical cable system includes a cable operating only in traction regardless of the direction of rotation of the steering wheel.
In a different arrangement of the mechanical connection, the mechanical cable system includes a cable operating in torsion and receiving and transmitting rotational movement of the steering wheel.
According to an embodiment of the invention, the mechanical cable system includes a traction cable on four pulleys mounted on the structure of the vehicle to form a loop which is connected to the upper connecting assembly and to the lower connecting assembly.
According to the invention, the upper connecting assembly can take various forms. In one arrangement, the upper connecting assembly comprises a pinion which meshes with a rack and is driven in rotation by the upper steering column part and the rack is attached to the mechanical cable.
In another arrangement, the upper connecting assembly consists of two take-up pulleys
which is driven in rotation by the upper steering column part,
and which has a groove receiving the corresponding end of the mechanical cable,
each cable end being attached to the groove of the corresponding pulley at a required location.
In another arrangement, the upper connecting assembly consists of a take-up pulley which is driven in rotation by the upper column part and has two grooves, each groove receives the corresponding end of the mechanical cable and each cable end is attached to the corresponding groove at the required location.
According to the invention, the lower connecting assembly can take various forms. In one arrangement, the lower connecting assembly consists of a mobile bearing fixed to the steering rack and passing through an opening in the housing of the steering rack and a fixed bearing attached to the housing of the steering rack and the end of the mechanical cable passes through the fixed bearing and is attached to the mobile bearing.
In another arrangement, the lower connecting assembly consists of a mobile bearing fixed to the steering rack and passing through an opening in the housing of the steering rack and two fixed bearings fastened to the housing of the steering rack-and on respective opposite sides of the opening and each end of the mechanical cable passes through the corresponding fixed bearing and is attached to the mobile bearing.
In another arrangement, the lower connecting assembly consists of two rack-and-pinion gears, namely a first gear with a first rack which is attached to the mechanical cable and which drives a first pinion and a second gear with a second pinion which drives a second rack attached to the steering rack, the first pinion and the second pinion are mounted on the same shaft and constrained to rotate together and the first pinion and the second pinion are such that displacement of the mechanical cable displaces the steering rack differently.
In one particularly beneficial embodiment of the mechanical connection in accordance with the invention, the mechanical cable system includes a traction cable with two runs on the same side of the vehicle and each of the two runs is connected to the upper connecting assembly and to the lower connecting assembly.
In this mechanical connection, the upper connecting assembly includes a gear whose first pinion is rotationally coupled to the upper steering column part and a sprocket meshing with a chain whose two ends are connected to corresponding upper ends of the two runs of the mechanical cable, the sprocket and the second pinion of the gear are mounted on the same shaft and constrained to rotate together and the first pinion and the second pinion are such that displacement of the mechanical cable is as small as possible for the required rotation of the steering wheel.
In this mechanical embodiment, the lower connecting assembly includes a sprocket meshing with a chain the two ends of which are connected to the corresponding lower end of two runs of the mechanical cable and the sprocket is mounted on the shaft of the pinion of the rack-and-pinion steering box.
In another embodiment, the lower connecting assembly includes a sprocket meshing with a chain whose two ends are connected to the corresponding lower end of the two runs of the mechanical cable, the sprocket is mounted on the shaft of the electric motor of the electrical connection and the electric motor drives the shaft of the pinion of the rack-and-pinion steering box.
With the above mechanical connection, the torque sensor is on the shaft of the pinion of the rack-and-pinion steering box, an actuator providing feedback between the steered wheels of the vehicle and the steering wheel is on the upper steering column part and the feedback actuator is electrically connected to the central control unit.
According to another embodiment of the invention, the mechanical cable system includes a cable operating in torsion, the upper connecting assembly consists of an end-piece at the corresponding end of the mechanical cable which has a recessed shape adapted to receive the end of the upper steering column part, the end has a projecting shape whose dimensions match the recessed shape of the end-piece, the lower connecting assembly consists of an end-piece at the corresponding end of the mechanical cable which has a recessed shape adapted to receive the end of the shaft of the pinion of the rack-and-pinion steering box and the end has a projecting shape whose dimensions match the recessed shape of the end-piece.
The electrical and mechanical steering system for automobile vehicles in accordance with the invention therefore has the advantage of no rigid mechanical connection between the steered wheels and the steering wheel. The above architecture eliminates all feedback of impact from the steered wheels to the steering wheel, which considerably improves the safety of the automobile vehicle. Also, the arrangement of the electrical connection with its central command and control unit for the force furnished by the electromechanical converter provides power steering matched to the driver and controlled return of the steering wheel to the center position.